1. Field of the Invention
The present invention relates to an indexable cutting insert releasably secured to, for example, cutting tools chiefly for use in surface cutting operation such as facing, peeling or the like, more particularly, to an indexable cutting insert capable of suppressing chattering generated during cutting.
2. Prior Art
FIGS. 1 to 3 depict a conventional indexable cutting insert 1 for cutting tools for use, for example, in facing an inner or outer surface of a cylindrically shaped workpiece. This cutting insert 1 is secured on a tool holder which is movable and rotatable relative to the workpiece.
The indexable cutting insert 1 is formed, by powder metallurgy process, in a parallelogramic plate. A cutting blade 2 is defined along the crossing line of a cutting surface 3 and a flank 4. On the flank 4, several nicks 5 are formed in parallel to each other, so as to extend in a direction perpendicular to the cutting blade 2, and each nick has a trapezoidal cross-section. Thus, cutting blade 2 is divided into blade segments 2a.
In the above-mentioned cutting insert 1, chips generated in cutting process are subdivided into pieces by blade segments 2a, and transferred through nicks 5, therefore, reacting force through cutting is decreased and chattering of the cutting insert 1 or cutting tool is suppressed. But, as a result of cutting blade's separation, edge portion 2b of blade segment 2a is inclined to crack or fracture, especially when the insert 1 is positive, i.e., the cross axes angle .alpha. between cutting surface 3 and flank 4 is acute, as is shown in FIG. 4, this tendency is more obvious.
In order to prevent such fracture of blade segment 2a during cutting 1A, a cutting insert as shown in FIGS. 5 to 7 is developed, wherein nicks 6 are formed of V type cross-section. In this type of cutting insert, the inner side surface 6a of nick has larger obtuse angle .beta. against flank 4, thus the edge portion 2b of each blade segment 2a has more durability against fracture than the previously mentioned conventional cutting insert. Although, as the rake angle .alpha. of the cutting insert is the same as shown in FIG. 4, appropriate improvement against fracture is impossible.
Another problem to be solved about the conventional cutting insert 1, 1A is that feed pitch of the workpiece to the cutting insert is limited within the depth of nick d. If feed pitch overcomes the depth of nick d, chip-subdividing function is suppressed, and cutting insert should lose above-mentioned anti-chattering effect. But, if the depth of nick should be set larger, not only each blade segment 2a but also the whole cutting insert loses stiffness.